Because it is motor neurons that invariably die in amyotrophic lateral sclerosis (ALS), most attention has focused on these cells as the primary site where pathophysiologic injury is initiated. However, evidence from human autopsy studies and a transgenic mouse model of familial amyotrophic lateral sclerosis, suggests a potential role for glia in the pathogenesis of disease. To address the cell specific origin of mutant (m) Cu/Zn superoxide dismutase (SOD1) induced disease, we have generated lines of transgenic mice using glial or neuronal specific promoters which allow expression of MSOD1 restricted to either neuronal or glial population. These lines do not develop motor weakness, raising the possibility that disease expression requires both neuronal and glial dysfunction induced by mSOD1. To test this hypothesis, we will determine whether crossing glial and neuronal restricted transgenic lines expressing mSOD1 will reconstitute the disease process in mice and lead to motor neuron degeneration. We will also use a spinal cord organotypic slice model of motor neuron degeneration to address specific mechanisms underlying interactions in fALS, we will generate chimeric mice from wild type and conventional mSOD1 mice, as well as derive chimera from conventional mSOD1 mice and either glial or neuronal specific mSOD1 transgenic liens. These experiments will determine whether glial/neuronal dysfunction involves cell-cell autonomous processes and ascertain whether the disease can be rescued by normal functioning glia. Although the exact mechanism of mSOD1 toxicity is still unknown, recent evidence has supported a critical role for zinc and copper ions. Because neurons and glia both express a repertoire of genes related to zinc/copper binding including the metallothioneins (MTs), we predict that both cell types will manifest abnormal MT expression patterns. In addition, we hypothesize that targeted deletion of neuronal or glial MT genes will significantly accelerate mSOD1- induced disease. Overall, these experiments will test the hypothesis that both neuronal and astroglial dysfunction is required for manifestation of disease in a transgenic murine model of fALS. These results will provide critical insights into mechanisms underlying human motor neuron disease and have important implications for future therapeutic interventions.